This corresponds closely to the anterior limb and, like it, is divisible into three parts, the thigh, the shin or crus and the pes.
As was the case with the anterior limb, all the long bones have their ends formed by prominent epiphyses which do not unite with the shaft till late in life.
In the thigh there is only a single bone, the femur.
The femur is a moderately long, slender bone with a well-ossified hollow shaft slightly curved in a sigmoid manner. Both ends are expanded, the proximal end is hemispherical and articulates with the acetabulum, the distal end is larger and more laterally expanded.
The shin likewise includes a single bone, the tibio-fibula, but this, as can be readily seen by the grooves at the proximal and distal ends of the shaft, is formed by the fusion of two distinct bones, the tibia and fibula. The tibio-fibula is longer and straighter than the femur.
The pes consists of two parts, the ankle or tarsus and the foot.
The tarsus consists of two rows of structures, very different in size. The proximal row consists of two long bones, the tibiale and fibulare, which are united by common epiphyses at the two ends, while in the middle they are widely separated. The tibiale lies on the tibial or pre-axial side, and the fibulare which is the larger of the two bones on the fibular or postaxial side. The distal row of tarsals consists of three very small pieces of calcified cartilage. The postaxial of these is the largest, it articulates with the second and third metatarsals and is probably homologous with tarsalia 2 and 3 fused. The middle one is very small, it articulates with the first metatarsal and is probably tarsale 1. The pre-axial one articulates with the metatarsal of the calcar, a structure to be described immediately, and has been regarded as a centrale.
The foot includes five complete digits and a supplemental toe as well. Each of the five digits consists of a long metatarsal with epiphyses at both ends, and of a variable number of phalanges. The first digit or hallux and the second have two phalanges, the third three, the fourth, which is the largest, four, and the fifth, three. The distal phalanges have epiphyses only at their proximal ends, the others at both ends.
On the pre-axial side of the hallux is the supplemental digit, the prehallux or calcar. It consists of a short metatarsal and one or two phalanges, and is terminated distally by a horny covering of epidermal origin.